Building control or monitoring systems often include an audio announcement system either integrated or closely associated therewith. Such announcement systems usually locate a number of output transducers, such as loud speakers, throughout a region being monitored. For example, a multiple story building might include a number of loud speakers on every floor of the building for purposes of providing announcements from a common location which might be associated with the building control or building monitoring systems.
Known audio announcement systems can provide both verbal messages which are generated in real-time by either an operator or electronically. Alternately, pre-stored messages can also be forwarded and disseminated via the pluralities of speakers located throughout the region of interest.
In known systems, hundreds of speakers can be connected to the output of a single audio amplifier. Those speakers each play the same message at the same volume. There are times when it would be desirable to be able to control individual speakers so as to, for example, direct messages through specific speakers or to override local volume controls to enable emergency messages to be broadcast at full volume.
It would be preferable if such functionality could be implemented so as to not require modifications to existing audio wiring, for installed systems, which is typically two conductor cables. It would also be desirable to be able to either upgrade or install speaker units which are transparent not only to the existing cabling but also to existing installed loud speakers which building management might want to maintain, at least in part.